Means for transmitting power electrically.



No. 881,864. PATENTED MAR. 10, 1908. G. LEWIN.

MEANS FOR TRANSMITTING POWER ELBCTRIGALLY.

, APPLICATION FILED JULY}. 1907.

6 SHBETS SHEET 1.

G. LBWIN.

MEANS FORTRANSMITTING POWER ELEGTRIGALLY.

AEPLIOATION FILED JULY 2,1907.

PATENTED MAR. 10, 1908.

6 SHEETS-SHEET 2- vwwv z No. 881,864. PATENTED MAR. 10, 1908.

' G. LEWIN.

MEANS FOR TRANSMITTING POWER ELECTRIOALLY.

APPLICATION FILED JULY 2, 1907.

6 SHEBTSSHEBT 3.

i-MW /Q.

PATBNTED MAR. 10, 1908' G. LBWIN. MEANS FOR TRANSMITTING POWERELBGTRIGALLY.

APPLICATION FILED JULY 2. 1907.

6 SHEETS-SHEET 4.

No. 881,864. 'PATENTED MAR. 10, 1908. G. LEWIN.

MEANS FOR TRANSMITTING POWER ELEGTRIGALLY.

APPLIGATION FILED JULY 2. 1907.

6 SHEETS-SHEETS.

N0. 881,864. PATENTED MAR. 10, 1908 G. LBWIN.

MEANS FOR TRANSMITTING POWER ELEGTRICALLY.

APPLICATION FILED JULY 2, 1907.

6 SHEETS-SHEET 6.

UNITED STATES PATENT. OFFICE.

GREGOR LEWIN, OF SCHONEBERQ NEAR BERLIN, GERMANY, ASSIGNOR TO SIEMENSSCHUCKERT-WERKE, G. M. B. H., OF BERLIN,

GERMANY, A CORPORATION OF GERMANY.

MEANS FOR TRANSMITTING POWER ELEC'I'BIGALLY.

, Specification of Letters Patent.

Patented. March 10, '1908.

Application filed July 2, 1907. Serial in. 881,906-

To all whom it may concern:

Be it'known that I, Gnneon LEWIN, engineer, a subject of the Emperor ofRussia, resident of Schoneberg, near Berlin, Germany, have invented'acertain'new and use ful Improvement in Means for Transmitting PowerElectrically, of which the following is a s ecification. he presentinvention relates to means for independently regulating a plurality ofelectric motors by means of one single separately excited controllinggenerator.

In electrical transmission of power plants the working of the same hasfrequently proved very preferable with such dynamos in which thegenerator is connected with the motor in such a manner that thearmatureof the motor ispermanently in series with the armature of thegenerator. The regulation of the motor, as well as the starting andstopping of the same, is only effected by-Lthe tGDSlOIl of theseparately excitedgenerator being variedfrom a positive maximum to zeroand then to a negative maximum by varyi the excitation of the enerator.The fie d winding of the separate y excited generator can thus be fedfrom a'battery of accumulators or froma special exciting ma,- chine.Such generators as above described arehereafter referred to ascontrolling generators. in this specification and in the claims belon'ng thereto. The conditions are frequent y such that a plurality ofelectric motors must, generall' speaking, simultaneously and uniform yreilated. In this case the motors are prefera l regulated by means ofone single contro ling dynamo, whereb under certain circumstances, asubstantia saving in space and cost of plant is effected. Particularlyon ships, for examqie, the saving in space which is made 'poss le bysuch an arrangement can be of considerable importance.

invention is means for regulat' continuous and alternate current motorsqulteindepend- .ently one of another as occasion requires, said motorsbeing driven, generally speaking, by one si 16 controlling generatoraccor in to the a ove definition;

he invention consists. substantially in providin means for varying theexciting current or; each electric motor which permits the number ofrevolutions of electric of the speed and of the direction of rotationNow an important object of the present;

motors to be varied inde endently of one another within ve wi e limits.These electric motors may e either series or shunt wound.

The electric motors which are to be regulated may be connected either inparallel or. in series. As, however, with parallel con- .nection, theregulation of-the electric motors is considerably more troublesome, andalso as the electric motors cannot be regulated so independently one ofanother and not within such Wide limits as in the case of series con-'nection, reference is as a rule given to connecti'ng t motors in series.

When the armatures of a plurality of motors are connected in series withthe armature of the controlling generator, the number of revolutions ofthe individual motors is regulated independently one of another by theirexcitation being varied. If the exciting current of the one motor isweakened, this will'not run quicker,'as would he the case if the motorwere connected singl with the d amo, but it will run slower. diminis 'ngstep by step the excitation 0 the individual motor, the s eed can beadually reduced to zero. g the direct on of rotation of a single motorcan be reversed by the exciting current being first brought to zero andby the field being then magnetized .in the opposite direction. Thenumber of revolutions of the other motors will increase simultaneouslywith the weakening of the field of the one motor, if the excitation ofthe -other motors isnot varied and the armature 90 tension of thecontrolling dynamo remains the same. .Ifthe number ofrevolutions ishowever tobe kept constant, either .the'field of the other electricmotors must be strengthened or the tension of the generator must be {)5I diminished, or both means may be employed simultaneously. This methoof regulation is of specially great value for ships, and particularl forsuch machines w 'ch are.

to be driven t e resistance of which to be overcome by the motor varieswith the number of revolutions. For ships an arrangement of such a kind1s 0 particularly great importance that the two pro ellers-are drivenbytwo electric motorswhic are .connected in series and driven in commonb one single controlling generator. The vantage lies in the em loyrnentof onesingle generator, which can e driven by a steam turb ne forexample, whereby space and 1 10 weight are saved. For example, if theship is to veer round, the excitation of the one electric motor isweakened, the consequence of which is that this motor and the propellercoupled with it runslower, and simultaneously the other electric motorand the appertaining propeller run faster. ening or weakening the fieldof the. second electric motor, its speed can be respectively increasedor diminished still more as desired. Further, it is possible at anytime, by varying the excitation of the current generator itself, tosimultaneously vary the tension generated by it and thereby the speed ofthe two motors in series with it. This uniform influencing of the twoelectric motors may be effected simultaneously with the individual relation of the same. It is thereby attamed that the speed with which theship is swung round can be varied within wide limits. The motors canalso beregulated at once in the above described manner by the onerunning in a direction opposite to the other, which is of specialimportance in driving ships. The speed of the other motor does notrequire in itself to be varied at all, and the current generatorlikewise does not require to be regulated, although it may be preferableto do so under certain circum stances, in order, for example, to preventthe generator being overloaded.

In order that the invention may he clearly understoood reference is madeto the accompanying drawings in which various embodiments are showndiagrammatically b way of example as applied to the driving oi ships proellers, for w 'ch p ose they are artic arly suitable, it being understooof course that they may also be employed for other urposes;

In t e drawi s:Figure 1 shows one arrangement, the eld windi s of twomotors in series with the generator eing connected with a commoncontinuous current system: Fig. 2 is a modification, the excitation ofthe .motors being controlled by other dynamos,

the latter being connected with a common continuous current system; Fig.3 is another modification of the arrangement shown in Fig. 1, theexcitation of the two motors being igs. 1

whereasFi 5 shows an arrangement similar tothat in ig. 2, alternatecurrent machines being employed, and Fi dis a modification of thearrangement in Fig. 5, two alternate current controlling generatorsbeing em- -plo ed.

eferring to the drawings, Fig. 1 shows generally an arrangement by whichtwo motors 'm and m connected in series and driving ships propellers s,and s, are regulated from the common controlling generator g. Thisgenerator is driven at constant speed By strengthby the prime mover t,for example a steam turbine. The tension of the generator g can bevaried between a positive and a negative maximum by varying theexcitation-of the field winding it by means of the regulating device 1.A continuous current system I is taken as the source of current for theexcitation. The excitation may also be effected by means of a specialexciting machine which is driven by the prime mover it. When the motorsare to be regulated in common and equally, this is efiected by means ofthe regulator 1'. But in order to be able to regulate the electricmotors independently one of another, in accordance with the presentinvention special regulators r, and 1', are rovided in the fieldcircuits of the motors y which the excitation of the field windings n,and n, of the two motors can bevaried between a positive and a negativemaximum in the above described manner. In the arrangement according toFig. 1 the system It li ewise serves as the source of current for theexcitation of the motors. In Fig. 2 an arrangement similar to tha shownin Fig. 1 is represented. The field windings of the motors 'm and m .arenot, however, connected directly with the system It, but with theexciting dynamos which are arranged specially for each motor on theshaft of the prime mover t. In this arran ement the motors are regulatedby the fie ds of the exciting machines'being regulated as desired bymeans of the re ulating switches r, and 1',. p The. tensiono? thecontrolling dynamo can be varied within optional limits by a regulatorr.

Animportant advantage of the arrangement of special exciting machines isthatthe regulation is effected by means of weak currents only, whichisparticularly advantageous when it is a question of motors ofconsiderable capacity, because in thisqcase the re ulating apparatus canhave small dimensions and the conductors which lead to these a paratuscan be very thin and can be convemently led to a-place at a considerabledistance from. which the control or regulation is effected, for examplethe bridge-deck on vboard ship. controlled by a common regulator; Fi 4is a i modification of-the arrangements in and-3, there being twogenerators provided;

It is preferable, when there are only two motors drivenby onecontrolling enerator, to combine the two switches r, and r, of thearrangement according to Figs. 1 and 2 to one single switching apparatus2, as represented in Fig. 3. By means of this arrangement only onehandle needs to be operated and therefore errors are avoided. Namely,the exclting currents of the two motors are revented from beingsimultaneously varier m such a manner that the speed of the motors wouldincrease in an undesirable manner. With this regulator, when the field nis weakened the field 11, is kept constant. The speed of the motor n, isreduced therefore i and that of m is increased. Butif the speed of m isto be reduced without the motor 'm running faster, this can be effectedby regulating the tension at the controlling generator 9 by means of theregulator r. The contacts a, and d 0, and (1,, and so on, are directlyconnected by conductors in the arrangement according to Fig. 3.

Instead. of the field windings of the motors being fed from thecontinuous current system as in the arrangement according to Fig. 3, anexciting machine can be arranged on the shaft of the prime mover foreach motor and the excitation of these exciting machines can be variedby means of one, common regulator. Further the importance of thearrangement in accordance with the present invention for plants on shipsliesalsoin the possibility wluch there is in these plants, in which twoprime movers and two generators are employed, of maintaining both themotors working with only one single generator at all times, even if atreduced speed, each set com rising one prime mover and one controllinggenerator being normally used for driving one I propeller. Such anarrangement is shown in Fig. 4. The controlling generators g, and g, andthe exciting machines e, and e, for the motors are arranged on theshafts of the prime movers t, and t,'. There are also dynalnos, d, andd, on the latter shafts which serve for feeding the field windings ofthe generators g, and g and the field windings of the exciting machinese, and e,.

With the switches 11 and p in the position shown the field of excitermachine e, is fed by dynamo d, through conductors 100, 101, 102, 103,104, 105, 106, 107, while the field of exciter machine e is fed bydynamod through conductors 108, 109, 110, 111, 112, 113, 114, 115. In thisposition of the switches u and p the controller 2 is entireiy cut out.The motors m, and m are regulated by controllers r, and 13,. If now itbe desired to shut down one of the prime movers t, or

t,, its corresponding clutch b, or b, is opened,

the switch p is closed, switch 11 thrown to the right, and switch u,- oru, thrown down. For example, supposing for some reason it be desired toshut down the prime mover t the clutch 6 is opened, the switch p closedand the switch 14 thrown to the right. Switch u, is thrown down, thusconnecting the armature of motor m in series with the armature of motorm both of which are then fed by generator g,. By throwing switch 11 tothe right it is obvious that conductors' 103 and 104 are nolonger'directly connected with conductors 102 and 105 but conductors 103and 104 are then connected with them through the controller z. Likewisethe conductors 111 and 112 are no longer directly connected withconductors 110 and 113, but are connected with them through thecontroller 2. The effect of closin the switch p is to connect the d namo(I, with the dynamo 11, across by con uctors 101, 114 and 100, 109, andsince the dynamo d, is no longer driven by the prime mover t,, ittherefore runs as a motor by current from dynamo (1,, and turns theexciter machine e Supposing the controller arm of controller 2: to be inthe position shown the fields of ex citers e, and e are both fed fromthe one dynamo (1,. Current leaves dynamo d by conductor 100 and passinthrough the switch p goes direct by cond uctors 114 and 115 throughfield and armature of dynamo d and back by conductors 108, 109, switchp, 106 and 107 to dynamo d,. Abranch circuit, however, leads fromconductor 101 by conductor 102 and returns to conductor 109 by conductor110. The current which leaves by conductor 102 passes through conductor116 to segment 117 of the controller 2 which is electrically connectedwith the upper, segment 118. The current then divides, one part passingthrough brush 120 and the other part passing down into ring 119. From118 the current takes the fol-' lowing course: brush 120, resistances 0to c, and i, to i,, conductor 121, switch 11, conductor 111, field ofexciter e conductor 112,

switch u, conductor 122, segment 123, brush 124, segment 125, conductor126, segment 127, conductor 128 and conductor 110 back to the originalcircuit, returning to d namo' d, by conductor 109, switch p and comuctors 106 and 107. Taking up the other branch from segment 118, thiscurrent passes down into ring 119, leaves by brush 129, passes throughresistance elements f,, to f conductor 130, switch a, conductor 104,field of exciter 2,, conductor 103, switch a, conductor 131, segment132, brush 133, inner ring 134, conductor 135, segment 127 and conductor110 back to original circuit at conductor 109. It is thus seen that thefields of exciters e, and e, are fed in parallel from the single dynamod, and can be re lated in-common by controller 1' It is a o apparentthat by moving the controller arm of controller 2 into a horizontalposition at the left the resistance between circle 119 and conductor 130would be diminished while at the same time the resistances betweensegment 118 and conductor 121- would be in creased. Therefore the fieldof exciter e, would be strengthened and the fields of exciter (2 beweakened. In this way the fields of the two exciters may be varied withrespect to each other.,

When the operating lever of rheostat 2 is moved into a position belowthe horizontal ment 118 and ring 119 and therefore art of the currentfrom segment 117 asses t ough these conductors and leaves t e ring 119by brush 129, which as before, leads throu h a resistance, in this caseterminal h an resistances f to f 5 for exam le, and passes through thesame circuit as efore described to the field of exciter e, in the samedirection as before and returns, as before, to the main circuitconductor 109. The other portion of the circuit, however, which branchesfrom segment 117, asses throu h brush 124 into segment 123, cm which t ecurrent travels in the opposite direction from before, through theconductor 122, switch a, conductor 112,

field of exciter e conductor 111, switch u, conductor 121, resistances ito 5,, and resistances c, to 0 terminal 4 (which is electricallyconnected with 0,), brush 120, segment 127, and back to original circuitbyconductor 110. Thus, field of exciter e, is reversed, while the fieldof exciter e, is energized as before.

To reverse the field of exciter e, without reversing the field ofexciter e, from its original direction, the controller arm is moved intoa osition below the horizontal on the right 0 the controller 2. vWhilein that position, current leaves the original circuit conductor 101 byconductor 102 and passes, as before, by conductor 116 into segment 117.From segment 117, current divides, as before, a art of it passes intocontact ring 119 througli the segment 118, which is electricallyconnected with ring 1.19 and segment 117. Contact ring 119, in thiscase, however, does not feed the field of exciter e, as in the two casesbefore, but now the current passes through brush 129 and throughresistance i i for example, and through conductor 121 switch u,conductor 111 field of excitere in the same direction as in the firstcase, conductor 1 12, switch u, conductor 122, segment 123, brush 133,contact ring 134, conductor 135, segment 127, and back, by

conductor 110, to the original circuit conductor 109. The other branchof the current, from segment 117, asses through brush 124 to segment132, t rou h conductor 131, switch u, conductor 103, t rough the fieldof exciter e in opposite direction from the first case, throughconductor 104, switch a, conductor 130, resistances f 5 to f 0 to 0 andcontact 9 to se ment 127 and back, by conductor 110, to t e originalcircuit conductor 109. It is thus seen that by 0 erating the controllerarm of controller 2,

t e current may firstbe maintained in normal direction for forwardrunning through the fields of exciters e, and e,, and var ed as to strenth in one relativel to the. other, and

. second, e reversed in fiel of exciter e, while maintained in normaldirection throu h field of exciter e,, and third, be reversed in saidfield exciter e, while maintained in nor- .ries.

. step by mal direction in field of exciter e It is obvious that byregulating the fields of the exciters e, and e,, the motors m, and m,with their corresponding pro ellers are caused to operate in any desiredirection and at any desired speed.

It is preferable that the motors work with weakened fields in order tobe able to utilize the energy supplied by the generator 9, as favorablyas ossible. Namely, in driving ships, the'wor dissipated by thepropeller is about pro ortional to the third power of the number 0revolutions. When the one generator is placed out of work the ca acityof the electric plant sinks to one ha what it was, and also the numberof revolutions of the two motors sinks to one half of that which obtainswhen they are connected in se- It follows from the above, however, thatat this reduced s eed'the contro generator 9 is not fu y utilized. Itsfu utilization will be obtamed by the electric motors being allowed torun faster, which is effected by simultaneously weakening the fields ofthe two motors. For this purpose the re lator 2 which is represented inFlg. 4 is so i rmed that in the 'excit" circuit of each motor additionalsteps 0 resistance 1 s) s s: and 9 fifuffzfsi and so suitable for theconditions 0 working are inserted when the lever of the switch is inthe. osition. If the motors are to be central regulate independently ofone another, more resistance c,-,-"c,, c 0,, and so on, or o, 0,, 0, 0,and so on, is'inserted in the circuit of that motor which is torunslower, and simultaneously the additional resistance is cut out stepother motor. turned from the central position to the one side, the onemotor runs at a maximum s eed, whereas the other is stationary.

en the lever of the switch is rotated 180,

in the exciting circuit of the If the lever of the switch is the numberof revolutions ofthe two motors is e ual, but the motors run in oppositedirections. .When the lover of the switch is turned to the other side,the reverse 'takes place. Thus when one generator is not working theplant can be kept running, even if with a correspondingly reduced s ed,without influencing the ca ability 0 'maneuverin Not. only-is. a at reacserve an increased security of operation obtained in the plant, but alsothe possibility of just as economic operation withv reduced speed aswith speed, which is of the greatest importance particularly formen-ofwar.

The propellers of ships can be driven not onlyby continuous currentmotors, as is rep resented in Figs. 1 to 4, but also by means ofalternate currentmotors in a similar way. In Fig; 5 such an alternatecurrent plant with separately excited shunt wound motors is hing re-.

the arrangement according to Fig. 2. The field of the controllinggenerator 9, in the circuit of which the two motors m and in, are

is of different phase from the alternate cnr rent of the main generator.The size of the angle of this difference of phase must be chosen, havingregard tothe average'diffen ence of phase in the plant, that the mostfavorable conditions are obtained both for runnin. the electric motorsand for continuity of wor in The exciting machines are rigidly couplewith the main generator correspond-. ing to the most favorable angle.When the motors are to be regulated independently of one another, thiscan be effected in the above described manner by the'regulators 1', andr, in the exciting current circuit of the dynamos 6 and e,.

In order to avoid the employment of special exciting machines, use maybe also be made of the arrangement according to Fig. 6. In thisarrangement the generator is sub-divided into two machines 9 and g,which are mechanically coupled with one another, and their armatureseach carry two armature windings (L, b,, or (1, 1),, which are dis lacedabout 90 degrees. The generators an motors are connected in series. Onlythe one generator, for example 9 can be regulated in its tension betweena positive and a negative maximum by means of the regulator r, the othergenerator. g being excited with constant current. The field winding ofthe motor m is excited by the winding 7), of the generator as thecurrent in this winding b, has a di erence of phase of about 90 degreesfrom that of the armature current. In thesame manner the field of m isexcited from the winding a, of the generaton'g Both the field windingsof the motors are thus connected to sources of current havinga constanttension, as the excitement of the dynamo 9 is not varied. The motors canbe regulated independently one of the other in (im optional mannerby theregulators 1', an r.

This connection according to Fig. .6 above described permits the motorsto be regulated in common and uniformly only in one direction ofrotation lrom a maximum to standstill. If the direction of rotation isto be capable of reversal, a reversing switchu must be arranged in thefield ma net circuit of the generator 9,, which switch 1s preferablyconnected mechanically with the regulator r in the exciting circuit ofthe generator 9,.

The motors employed in the above de- The fields of the excited motors.The plant is however less efficient the motorsare .regulated in thatcase by resistances connected in parallel with their eld windings 'andofcourse these resistances; must be proportioned for large strengths 'ofcurrent, mid-accordingly dissispate much energy, and moreover requireconductors leading to them ofconsiderable size. It is known that thearmatures of motors have hitherto been" put-in series in aconstant-current circuit which is entirely independent of the fields,each field being provided 'witha regulator." Such an arranges ment inwhich a constant-current generator is used differs substantially fromthat in accordance with the present invention employing one or morecontrolling generators of the type described, and I do not claim thesame broadly.

What I claim asmy, invention and desire to secure by Letters Batent is2- 1. In means for transmitting power electrically, the combination witha separately excited controlling generator and means for varying thefield. excitation of the same of a plurality of motors, an armaturecircuit in which the armatures of said motors are connec'ted in serieswith each other'and with the armature of said controlling generator,means for exciting'the fields of said motors independently of thetension in said. armature circuit and reversible means for varying thefield excitation of each of said motors independently of the other. r

2} In means for transmitting power'elecm trically, the combination-witha separately excited controlling generator and means for varying thefield excitation of the same; of a pluralityof motors, a plurality ofpropellers operativl connected with and adapted to -be driven y saidmotors, an armature circuit in which the armatures of said motors areconnected 1n series with the armature of said controlhng generator,means for excltin the fields of said motors independently o the Itension msald armature circuit and means plurality of motors, aplurality of ropellers operatively connected with and a apted to bedriven by said motors, an armature circuit in which the armatures ofsaid motors are connected in series with eachother and with the armatureof said controlling generator, means for exciting the fields of saidmotors independently of the tension in said armature circuit and meansfor varying the field excitation of each of said motors independently oftheother.

i. in means for transmitting power electrically, the combination with aseparately excited controlling generator and means for varying the fieldexcitation of the same, of a plurality of motors, a plurality ofpropellers operatively connected with and adapted to be driven by saidmotors, an armature circuit in which the armatures of said motors areconnected in series with the armature of said controlling generator,means for exciting the fields of said motors independently of thetension in said armature circuit and reversible means for varying thefield excitation of each of said motors independently of the other.

5. In means for transmitting power electrically, the combination with aseparately excited controlling generator and means for v rying the iieldexcitation of the same, of a plurality of motors, a plurality of"propellers operatively connected with and adapted to be driven by saidmotors, an armature circuit in which the arniatures of said motors areconnected in series with each other and with the armature of saidcontrolling generator, means for exciting the fields of said motorsindependently of the tension in said armature circuit and reversiblemeans for varying the field excitation of each of said motorsindependently of the other.

' 6. In means for transmitting power electrically, the combination witha controlling generator, having separate field coils, a

source of current, and irreversible regulator in circuit with saidfield-coils and said source of current, of a plurality of motors, havingse arate field-coils, an armature circuit in w rich the armatures ofthese motors are con nected in series with the armature of saidgenerator, a plurality of separately excited generators, each armatureof the-latter being in series with one of said field-coils of themotors, and a plurality of reversible regulators connectingeach of thefield-coils of -the latter generators with said source of current,whereby said motors can be regulated by varying the tension of saidcontrolling generator as well as by varying their own excitation.

7. In means for transmitting power electrically two controllinggenerators, two motors, driving two propellers, and two reversingswitches, the armatures of said gen erators being each normallycongected di rectly in series with only one armature of said motors andadapted to be cut out of circuit by said switches, thereby connectingthe armature of the other generator in series in one armature circuitwith the two armatures of said motors, in combina'tionwith separatemeans for exciting each of said generators, means forwarying theexcitation eiiected by the latter means and means for regulating thefields of the motors independently of each other and of the armaturecircuit, whereby when one of said controlling generators is cut out ofcircuit said motors can be regulated by varyin the tension of the othergenerator as well as by varying their own excitation.

8. In means for transmitting power electrically, two controllinggenerators, two motors, driving two propellers, and two reversingswitches, the 'annatures of said generators being each normallyconnected through said switches directly in series with only onearmature of said motors and adapted to be cut out of circuit bysaid-switches thereby connecting the armature of the other generator inseries in one armature circuit with the two arniatures of said motors,in combination with separate field-coils for each of said generators, asource of current, revers1ble regulators connecting each of saidgeneratorfield-coils with the latter, separate field-coils for eachmotor, niotor-exciting generators having separate "field-coils and eachhaving their armature connected with one of said motor field-coils, anda reversible regulator connecting the field-coils of the motor-excitinggenerator with said source of current, whereby when one .of saidcontrolling generators is cut out of circuit said motors can beregulated by varying the tension of the other generator as well as byvarying their own excitation.

In testimony whereofil have signed my name to this specification in thepresence of 100 the two subscribing witnesses.

GREGOR LEWIN.

Witnesses WOLDEMAR HAUPT, Iinnnr Hasrnn.

